This is from the NFL but is approximately correct for the NHL. The decline in value from pick to pick is greater in the NHL. In the NFL, players use draft position as leverage in contract negotiations, and aren't paid a basically fixed amount on an entry level contract.

Obviously it doesn't take into account the specific players in the draft year, such as the difference between Ovechkin and Malkin and that between Malkin and BarkerLadd/etc..